The present disclosure is directed to exercise equipment and more particularly to a set of stacked rotatable discs. Conventional stacked rotatable discs include a first disc that rests on a flat support surface such as a floor. A second disc is rotatably stacked and fastened onto the first disc so as to remain aligned with the first disc as the second disc is rotated via bearings about a central axis perpendicular to the support surface by a portion of a user's body supported on the second disc. Typically the stacked rotatable discs are used in pairs. For example, a user can stand or kneel on a pair of the stacked rotatable discs and twist his or her body during an exercise, causing the second discs to rotate relative to the first discs. If the stacked discs are large enough in diameter, a user can stand or kneel on the second disc of a stacked disc set while exercising. As the user twists her body the second disc rotates relative to the support surface. These conventional rotatable discs are free to rotate relatively to each other. Their use in physical exercise regimens is limited to the agility of the user and the particular movements required.
The bearings separating the first and second disc are typically sandwiched between sheet metal plates that are interlocked together and each fastened to one of the first or second discs. Alternatively each of the bearings may be carried in an opening in an annular plastic frame that is fastened to the first and second disc via a central axial bolt that holds the frame and first and second disc together. One problem with this configuration is that dynamic side loads on the second disc relative to the first disc can be large enough such that one or more of the bearings may be dislodged from its frame, rendering the stacked set either jammed together or limited in movement between the discs. Another limitation with conventional stacked rotatable discs is that there is no rotational resistance provided between the discs such that they cannot be utilized for strengthening exercises beyond generating a momentary torque that a user can apply during body rotation.